The following background commentary is an aid to understanding the present invention. Inclusion of this commentary is not an admission concerning the nature or content of the prior art.
Dipeptidyl peptidase-IV (DPP-IV) is a serine protease that belongs to the group of post-proline/alanine cleaving amino-dipeptidases. DPP-IV preferentially catalyzes the release of an N-terminal dipeptide from proteins with N-terminal penultimate proline or alanine.
The physiological roles of DPP-IV are diverse. DPP-IV is believed to play an important role in neuropeptide metabolism, T-cell activation, gastric ulceration, functional dyspepsia, obesity, appetite regulation, impaired fasting glucose (IFG), and diabetes. In particular, DPP-IV has been implicated in the control of glucose metabolism because its substrates include the insulinotropic hormones, glucagon like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP), which are inactivated by removal of their two N-terminal amino acids.
In vivo administration of synthetic inhibitors of DPP-IV prevents N-terminal degradation of GLP-1 and GIP, resulting in higher plasma concentrations of these hormones, increased insulin secretion and, therefore, improved glucose tolerance. Therefore, such inhibitors have been proposed for the treatment of patients with type II diabetes, a disease characterized by decreased glucose tolerance and insulin resistance.
Post-proline/alanine cleaving amino-dipeptidases have been discovered, including DPP-VII, DPP-VIII, DPP-IX, and fibroblast activation protein (FAP), that have the substrate- and inhibitor-specificity of DPP-IV. Thus, it has become clear that inhibitors of this sort may affect multiple members of the enzyme group.
The precise physiological role of each of these post-proline/alanine cleaving enzymes is not well defined. Consequently, inhibiting each of them separately, a subset of them, or all of them at the same time would have uncertain physiological effect(s).
Diabetic dyslipidemia is characterized by multiple lipoprotein defects, including moderately high serum levels of cholesterol and triglycerides, small LDL particles, and low levels of HDL cholesterol. The results of recent clinical trials reveal beneficial effects of cholesterol-lowering therapy in diabetic and nondiabetic patients, thus supporting increased emphasis on treatment of diabetic dyslipidemia. This need for intensive treatment of diabetic dyslipidemia was advocated by the National Cholesterol Education Program's Adult Treatment Panel III.
Obesity is a well-known risk factor for the development of many very common diseases such as atherosclerosis, hypertension and diabetes. The incidence of obese people and thereby also these diseases is increasing throughout the entire industrialized world. Except for exercise, diet and food restriction no convincing pharmacological treatment for reducing body weight effectively and acceptably currently exist. However, due to its indirect but important effect as a risk factor in mortal and common diseases it will be important to find treatment for obesity or appetite regulation. Even mild obesity increases the risk for premature death, diabetes, hypertension, atherosclerosis, gallbladder disease and certain types of cancer. In the industrialized western world the prevalence of obesity has increased significantly in the past few decades. Because of the high prevalence of obesity and its health consequences, its prevention and treatment should be a high public health priority.
At present a variety of techniques are available to effect initial weight loss. Unfortunately, initial weight loss is not an optimal therapeutic goal. Rather, the problem is that most obese patients eventually regain their weight. An effective means to establish and/or sustain weight loss is the major challenge in the treatment of obesity today.
Accordingly, a need exists for compounds that are useful for inhibiting DPP-IV without suppressing the immune system.
Several compounds have been shown to inhibit DPP-IV, but all of these have limitations in relation to the potency, stability, selectivity, toxicity, and/or pharmacodynamic properties. Such compounds have been disclosed, for example, in WO 98/19998, WO 00/34241, U.S. Pat. No. 6,124,305 (Novartis AG), and WO 99/38501 (Trustees of Tufts University).